Background Cross-education (CE) is being studied for several decades and refers to the power transfer and proprioception in untrained limb after training of the homologous contralateral limb.

Objective To examine whether unilateral strengthening of lower limbs with Thera-Band^® elastic resistance bands is beneficial also for the untrained contralateral limb in functional ability and balance.

Design A double blinding randomized prospective study.

Setting The study was conducted in the Department of P.E and Sports, Democritus University of Thrace, Greece.

Participants 15 healthy physically active students (at least three training per week) were randomly selected to participate.

Interventions The participants performed strength training with progressive overload for lower limbs, for 4 weeks, with frequency 3 times per week (12 sessions), duration of 30 minutes with 10 min warm up, 20 min strengthening exercises with Bands (Thera-Band^®) of quadriceps, hamstrings and gastrocnemius muscles. The exercises were executed at stations from supine, lateral and sitting position (4 sets of 10 reps with 15 sec break between sets).

Main outcome measurements A. Balance performance (total stability index as dependent variable of the Biodex Stability test) and b. functional ability (Single leg triple jump hop for distance with distance as dependent variable) at 3 times, before exercise period (pre), at the end (post) and 2 weeks after (retention). The hypothesis was formulated before data collection.

Results One way repeated measures Anova revealed improvement for both limbs: a. Stability index trained pre 5.87±1.15, post 3.44±1.11, retention 3.61±1.12 untrained pre 5.90±1.82, post 3.61±1.61, retention 3.20±1.71 b. Triple jump trained pre 3.70±.89, post 4.06±.91, retention 4.01±.88, untrained pre 3.78±.83, post 4.09±.85, retention 4.12±.71.

Conclusions Unilateral strength training with Thera-Band® elastic resistance bands at lower limbs is effective in improving functional ability and balance of untrained limb.